The present invention relates to a thin film photoelectric conversion module and a method of manufacturing the same, particularly, to a thin film photoelectric conversion module having a plurality of thin film photoelectric conversion cells connected in series and a method of manufacturing the same.
In general, a thin film photoelectric conversion module comprises a plurality of band-like thin film photoelectric conversion cells arranged in the direction of the short axis of the cell and connected to each other in series. In general, such a module is not used singly and is used generally in the form of a module array consisting of a plurality of modules connected in series or in parallel.
Where a leaf or bird droppings are attached to the light-receiving surface of a certain thin film photoelectric conversion cell included in such a thin film photoelectric conversion module, the light to the particular cell is partially or entirely intercepted so as to decrease the photoelectromotive force, leading to a marked reduction in the output of the entire module. It should be noted that the cell with the decreased photoelectromotive force acts as a diode connected in series in the reverse direction to the direction of the power generation, i.e., in the reverse direction to the direction in which the current generated by the photoelectric conversion flows. As a result, the light-intercepted cell exhibits a very high resistance, leading to the marked reduction in the output of the entire module as pointed out above.
The decreased photoelectromotive force of the cell affects not only the particular module but also the module array. More specifically, the module including a cell whose photoelectromotive force is decreased causes the output of the module array to be lowered markedly.
A measure for overcoming the problem is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 57-53986. Specifically, it is disclosed that a plurality of thin film photoelectric conversion cells connected in series are divided into a plurality of series arrays, and that these series arrays are connected in parallel. The particular technique makes it possible to prevent the output of the module array from being lowered markedly even if the photoelectromotive force of any of the cells has become zero. Also, in order to prevent the output of the module array from being lowered markedly, another measure such as mounting a single bypass diode to every module is known.
However, an additional problem is produced by the attachment of, for example, a leaf to the thin film photoelectric conversion cell, as follows. Specifically, if voltage higher than the withstand voltage is applied to the cell having the light thereto intercepted by the attached leaf or the like, an insulation breakdown is generated. Current does not flow uniformly through the cell of the particular state so as to bring about a local heating called a hot spot phenomenon. The local heating does not produce a serious problem where the current flowing through the cell is small. However, a module having a large area generally produces a large output current, with the result that, in the conventional module having a large area, the light-intercepted cell is heated to a very high temperature.